Method pertaining to an scr system and an scr system

ABSTRACT

For an SCR system for a motor vehicle ( 100; 110 ), the vehicle including a feed device ( 230 ) to feed reducing agent from a container ( 205 ) to a dosing unit ( 250 ) for supply of reducing agent to an exhaust duct of the vehicle ( 100; 110 ); a method of controlling the dosage of the dosing unit ( 250 ) by a pressure (Pr) at which reducing agent is dosed, and/or controlling pressure (Pr) of a rotation speed (RPM) of the feed device ( 230 ). Also a computer program product with program code (P) for a computer ( 200; 210 ) for implementing the method. Also an SCR system and a motor vehicle ( 100, 110 ) equipped with the SCR system.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a 35 U.S.C. §§371 national phase conversionof PCT/SE2012/051367, filed Dec. 10, 2012, which claims priority ofSwedish Patent Application No. 1151192-0, filed 14 Dec. 2011 and SwedishPatent Application No. 1251409-7, filed 12 Dec. 2012, the contents ofwhich are incorporated by reference herein. The PCT InternationalApplication was published in the English language.

TECHNICAL FIELD

The present invention relates to a method pertaining to an SCR system.The invention relates also to a computer program product comprisingprogram code for a computer for implementing a method according to theinvention. The invention relates also to an SCR system and a motorvehicle equipped with the SCR system.

BACKGROUND

Vehicles today use, for example, urea as reductant in SCR (selectivecatalytic reduction) systems which comprise an SCR catalyst in whichsaid reductant and NOx gas can react and be converted to nitrogen gasand water. Various types of reductants may be used in SCR systems.AdBlue is an example of a commonly used reductant.

One type of SCR system comprises a container which holds a reductant.The SCR system has also a pump arranged to draw said reductant from thecontainer via a suction hose and supply it via a pressure hose to adosing unit situated adjacent to an exhaust system of the vehicle, e.g.adjacent to an exhaust pipe of the exhaust system. The dosing unit isarranged to inject a necessary amount of reductant into an exhaustsystem upstream of the SCR catalyst according to operating routineswhich are stored in a control unit of the vehicle.

There is a constant need to reduce the amount of emissions from enginesof motor vehicles, not least in the case of heavy vehicles such astrucks and buses, in the light of continually tighter legal requirementsfor ever smaller emissions.

There are various ways of reducing emissions from motor vehicles

US2011239625 describes a device for injecting reducing agent in anexhaust system. The specification is concerned with ensuring thatreducing agent dosage is correct and is adjusted on the basis inter aliaof surrounding pressure. A specified pressure is set which depends onsurrounding pressure and the reducing agent dosage is controlled bysetting the length of time when the dosing valve is open.

US2011232267 describes a method and a device for dosing of reducingagent in an exhaust system. The reducing agent has to be added to theexhaust system in an evenly divided form. A desired drop size isdetermined on the basis of at least one exhaust parameter, followed bysetting a pressure as a function of the desired drop size. The exhaustparameters on which the desired drop size is based comprise at least onefrom among volumetric flow, flow velocity, mass flow, gas temperatureand gas pressure.

WO2006050318 describes a method and a device for dosing of reducingagent in an exhaust system. To adapt the reducing agent dosage to alloperating situations it is also possible to add vaporised reducing agentto the engine. The amount of reducing agent dosed is based on apredetermined optimised amount of reducing agent, the temperature of theexhaust gases and how the engine is running.

US2005235632 describes a device and a method for injecting a reducingagent into an exhaust flow in order to reduce emissions from an engine.To achieve as small drops as possible, a swirl plate [0013] is used. Toinject a certain amount of reducing agent which depends on the engine'sspeed, the temperature of the exhaust gases, exhaust flow, exhaustpressure, when the engine fuel supply takes place and desired NOxreduction, the dosage is controlled by adjusting the length of time whenthe injection takes place, i.e. the time when the valve (22) in thedosing unit 16 is open, at a predetermined specified pressure of thereducing agent.

EP1291498 describes a device for controlling emissions from an engine byinjecting a fuel in an exhaust system. The fuel is injected in the formof drops of controlled size. Their diameter is determined on the basisof the temperature of the exhaust gases or on the basis of thetemperature in the middle of the catalyst. To control the dosage, anelectronic control unit (ECU) controls the amount of reducing agentwhich is to be supplied.

US2009301067 describes a device for reducing agent dosing into anexhaust flow of a combustion engine, which takes place according to twodifferent schemes depending on the engine's operating state.

SUMMARY OF THE INVENTION

There is a constant need to improve today's SCR systems in order toreduce the amount of undesirable emissions from a combustion engine.

One object of the present invention is to propose a novel andadvantageous method for improving the performance of an SCR system.

Another object of the invention is to propose a novel and advantageousSCR system and a novel and advantageous computer program for improvingthe performance of an SCR system.

One object of the present invention is to propose a novel andadvantageous method for reducing the amount of undesirable emissionsfrom a combustion engine.

A further object of the invention is to propose an alternative methodpertaining to an SCR system, and an alternative computer programpertaining to an SCR system and an alternative SCR system.

These objects are achieved with a method pertaining to SCR systems for amotor vehicle according to the invention.

One aspect of the invention proposes a method pertaining to SCR systemsfor a motor vehicle, comprising a feed device to feed reducing agentfrom a container to a dosing unit for supply of said reducing agent toan exhaust duct of the vehicle. The method comprises the step ofcontrolling the dosing unit's dosage by means of a pressure at whichreducing agent is dosed.

One aspect of the invention proposes a method pertaining to SCR systemsfor a motor vehicle, comprising a feed device to feed reducing agentfrom a container to a dosing unit for supply of said reducing agent toan exhaust duct of the vehicle. The method comprises the step ofcontrolling the dosing unit's dosage by means of a pressure at whichreducing agent is dosed, which pressure is controlled by control of arotation speed of said feed device.

Flexible dosing of reducing agent in an SCR system is thus madepossible. A relatively high working pressure of said reducing agentgenerally results in a drop size distribution with more smaller dropswhich can more readily be captured in an exhaust flow from the vehicle'sengine. A relatively low working pressure of said reducing agent maygenerally result in a drop size distribution with more larger drops witha higher kinetic energy which are not affected by the exhaust flow inthe same way as smaller drops. Smaller drops are advantageous in certainoperating situations, e.g. at lower exhaust temperatures a smaller dropmay vaporise relatively quickly in the exhaust flow. In anotheroperating situation where a large amount of thermal energy is stored inthe exhaust system, larger drops are advantageous in that they can forexample be directed towards a surface of the exhaust system. Varyingdrop sizes are advantageous in certain cases where certain dropsvaporise relatively quickly in the exhaust flow and other drops are forexample directed towards various surfaces in the exhaust system. Thisresults in improved performance of the SCR system.

By suitably varying the working pressure according to the invention,e.g. on the basis of inherent characteristics of the dosing unit, it ispossible with advantage to alter in desirable ways a cone angle for thereductant dosed. In an analogous way this may be employed to optimisethe pattern of encounter between and/or mixing of reducing agent andexhaust gases. By altering a working pressure of the SCR system it isalso possible to influence the velocity of the reducing agent drops.This results in substantially the same advantages as described above.

The dosing unit may be configured to comprise an aperture and a needle.The needle covers the aperture when the dosing unit is not dosingreducing agent in the exhaust duct. For reducing agent dosing, theneedle moves away from the aperture, allowing the reducing agent to bedosed in the exhaust duct. The needle may be used to adjust the degreeof opening of the dosing unit. The dosing unit may alternativelycomprise an aperture of adjustable size to be further able to controlthe reducing agent dosage. As a further alternative, the aperture may bedirectionable for further potential control of the dosing of thereducing agent into the exhaust duct.

The method may comprise the step of controlling the dosing unit's dosageby means of the pressure on the basis of a prevailing temperature of asurface or component of said exhaust duct.

Controlling the dosing unit's dosage by means of the pressure at whichreducing agent is dosed thus makes it possible to influence anassociated drop size distribution. This may greatly affect a degree ofconversion of NO_(x) in the SCR catalyst.

The method may comprise the step of controlling the pressure at whichreducing agent is dosed by controlling a rotation speed of said feeddevice. This results in an accurate method pertaining to an SCR systemaccording to one aspect of the invention. Said speed may be controlledwith very great accuracy, making it possible for a working pressure ofsaid reducing agent in the SCR system to be also controlled with greataccuracy.

In one aspect of the present invention, the pressure may be variedduring an opening phase of the dosing unit. This may be advantageous inthat the drop size distribution of the reducing agent at the beginningand end of an opening phase of the dosing unit, with a constant pressureof the reducing agent, may differ from the drop size distribution duringthe remainder of the opening phase. The drop size distributionthroughout the opening phase may be controlled by varying the pressureduring it. In certain operating situations it is desirable to have auniform drop size distribution throughout the opening phase, which maybe achieved by applying a certain pressure at the beginning and end ofan opening phase and a different pressure during the remainder of theopening phase. In certain operating situations it may be desirable formore larger or smaller drops of reducing agent to be dosed at thebeginning than at the end of the opening phase. Alternatively, thepressure during an opening phase may be kept constant but vary betweenopening phases.

In one version the method may comprise the step of controlling thepressure at which reducing agent is dosed by controlling a displacementof a piston pump incorporated in said dosing unit.

The dosing unit may take the form of any desired pump, e.g. a diaphragmpump or a gearwheel pump.

The method may comprise the step of controlling the pressure by alteringa constriction in a reducing agent feedback line from the dosing unit tosaid container. This results in an accurate method pertaining to an SCRsystem according to one aspect of the invention. Said constriction maybe altered with very great accuracy, making it also possible for aworking pressure of the SCR system to be controlled with great accuracy.A robust method may thus reliably be achieved.

In one embodiment example a pressure of said reducing agent may becontrolled by controlling not only a rotation speed of said dosing unitbut also a constriction in a reducing agent feedback line from thedosing unit to said container. The result is an accurate methodpertaining to an SCR system according to one aspect of the inventionwhereby advantageous synergy effects are achieved. Simultaneouslycontrolling both a rotation speed of said dosing unit and altering saidconstriction makes it possible for the pressure to build up quickly.

The method may comprise the step of controlling the pressure by alteringthe configuration of the dosing unit, resulting in an accurate methodpertaining to an SCR system according to one aspect of the invention.Said configuration may be altered with very great accuracy, making italso possible for a working pressure of the SCR system to be controlledwith great accuracy. A robust method may thus reliably be achieved.

The method may comprise the step of controlling the dosing unit's dosageby means of the pressure on the basis of a prevailing temperature of asurface in the exhaust system. It may comprise the step of controllingthe dosing unit's dosage by means of the pressure on the basis of aprevailing temperature of a surface in the exhaust system where reducingagent dosed vaporises. It may comprise the step of controlling thedosing unit's dosage by means of the pressure on the basis of aprevailing temperature of a suitable surface in the exhaust system. Itmay comprise the step of controlling the dosing unit's dosage by meansof the pressure on the basis of a prevailing temperature of a suitablecomponent of the exhaust system, e.g. a vaporisation module, a particlefilter or said SCR catalyst. Improved performance of the SCR system maythus be achieved.

Said surface may comprise various parts of the exhaust system where thereducing agent vaporises. It may for example be a surface towards whichthe dosing unit's nozzle is directed in the exhaust system. It may alsobe a surface downstream of the dosing unit where reducing agent iscarried by the exhaust flow. It may be a surface of a vaporisation unitsituated downstream of the dosing unit in the exhaust system. It may bea surface which reducing agent dosed encounters.

The temperature of said surface or component may be detected by means ofa temperature sensor situated at or close to said surface where thereducing agent vaporises. The temperature of said surface or componentmay be detected by a temperature sensor situated on or in the immediatevicinity of said surface where the reducing agent vaporises. In certaincases it is advantageous to have a sensor on an outside surface of theexhaust system to prevent sensor wear. In certain cases this temperatureis that of an inside surface of the exhaust system. In other cases thetemperature of said inside surface may be calculated on the basis of ameasured temperature of the outside surface. Alternatively, a prevailingtemperature of said inside surface may be calculated on the basis ofother parameters, e.g. prevailing temperature of an exhaust flow from anengine, prevailing mass flow of exhaust gases from an engine, amount ofreducing agent dosed and the characteristics and state of the reducingagent, e.g. its chemical composition and prevailing temperature at thetime of dosing.

The method may comprise the step of controlling the dosing unit's dosageby means of the pressure on the basis of a prevailing temperature of anexhaust flow from an engine and/or a prevailing mass flow of exhaustgases from an engine. Improved performance of the SCR system may thus beachieved. A versatile method pertaining to an SCR system is thus alsoachieved, since alternative versions are possible. A prevailing massflow of the exhaust gases may be calculated by a control unit of thevehicle, e.g. using the engine's air intake and fuel intake asparameters. Alternatively, the mass flow of the exhaust gases may bemeasured by means of a mass flow sensor. As temperature sensors arerelatively inexpensive, a cost-effective method is also achievedaccording to one aspect of the invention.

The method may comprise the step of controlling the dosing unit's dosageby means of the pressure on the basis of a prevailing temperature of asurface in an exhaust pipe of the vehicle.

The method may comprise the step of controlling the dosing unit's dosageby means of the pressure on the basis of a prevailing temperature of airsurrounding the vehicle. This entails having to install temperaturesensors on the vehicle in a suitable way if none has already beeninstalled.

The method may comprise the step of controlling the dosing unit's dosageby means of the pressure on the basis of previous operating situationsof the vehicle. This entails a control unit of the vehicle usingcalculations according to a stored model as a basis for controlling thedosing unit's dosage in a suitable way by means of the pressure.

The method may comprise the step of controlling the dosing unit's dosageby means of the pressure and a dosing cycle rate, resulting in a methodpertaining to an SCR system with improved performance. Combined controlof the dosing unit's dosage by means of the pressure of the reductantduring dosing and making changes to a prevailing cycle rate of the SCRsystem makes it possible to achieve an optimised spray pattern of saidreducing agent dosed. The cycle rate may for example be within a rangeof 1-10 Hz. During a cycle, the dosing unit's opening period may bedetermined to regulate the amount of reducing agent dosed during saidcycle. The amount of undesirable emissions from the vehicle's engine maythus be advantageously reduced.

The method may comprise the step of varying the pressure of thereductant within a range of 1-15 bar. In one version the method maycomprise the step of varying the pressure of the reductant within arange of 7-13 bar. In one version the method may comprise the step ofvarying the pressure of the reductant within a range of 10-50 bar. Inone version the method may comprise the step of varying the pressure ofthe reductant within a range of 100-300 bar. In one version the methodmay comprise the step of varying the pressure of the reductant withinany suitable range. The result is a robust method whereby a workingrange is defined beforehand, eliminating risks of undesirable spraypatterns caused by too low or too high working pressure. Anoperationally safe and reliable method pertaining to an SCR system isthus achieved according to one aspect of the present invention.

The method may comprise the step of varying the pressure of thereductant steplessly during said control of the dosing unit's dosage,thus achieving a method whereby a desired spray pattern of saidreductant may be set in a well-defined way. A method for an SCR systemwhereby a desired mixture of exhaust gases and reducing agent may be setwith very great accuracy is thus advantageously achieved.

The method may further comprise the step of varying the pressure of thereductant, in discrete steps during said control of the dosing unit'sdosage, resulting in a method for an SCR system which involvesrelatively simple programming routines. Providing control of the dosingunit's dosage on the basis of discrete settable steps of the workingpressure makes it possible for a rotation speed of the feed device to bedirected towards predetermined set-point values, affording the advantageof data processing which involves fewer calculations.

The method may comprise the step of altering a dosing cycle ratesteplessly, resulting in a method whereby a desired spray pattern ofsaid reductant may be set in a well-defined way. A method pertaining toan SCR system whereby a desired mixture of exhaust gases and reducingagent may be set with very great accuracy is thus advantageouslyachieved.

The method may comprise the step of altering a dosing cycle rate indiscrete steps during said control of the dosing unit's dosage.Providing control of the dosing unit's dosage on the basis of discretesettable steps of the cycle rate makes it possible for a rotation speedof the feed device to be directed towards predetermined set-pointvalues, affording the advantage of data processing which involves fewercalculations.

The method may comprise the step of controlling the dosing unit's dosageby means of the pressure of the reductant and a dosing cycle rate on thebasis of a prevailing exhaust temperature and/or a prevailing mass flowof exhaust gases from an engine of the vehicle.

It should be noted that the method may incorporate one or more of theabove features in suitable combinations.

The method is easy to implement in existing motor vehicles. Softwarepertaining to an SCR system according to the invention may be installedin a control unit of the vehicle during the manufacture of the vehicle.A purchaser of the vehicle may thus have the possibility of selectingthe function of the method as an option.

Software which comprises program code for an SCR system according to theinvention will be easy to update or replace. Moreover, different partsof the software which contain the program code may be replacedindependently of one another. This modular configuration is advantageousfrom a maintenance perspective.

One aspect of the invention proposes an SCR system for a motor vehicle,comprising a feed device to feed reducing agent from a container to adosing unit for supply of said reducing agent to an exhaust duct of thevehicle, comprising means for controlling the dosing unit's dosage bymeans of a pressure at which reducing agent is dosed, and means forcontrolling the pressure by control of a rotation speed of said feeddevice.

One aspect of the invention proposes an SCR system for a motor vehicle,comprising a feed device to feed reducing agent from a container to adosing unit for supply of said reducing agent to an exhaust duct of thevehicle. The SCR system comprises means for controlling the dosingunit's dosage by means of a pressure at which reducing agent is dosed.

The SCR system may further comprise means for controlling the pressureby control of a rotation speed of said feed device.

The SCR system may comprise means for controlling the dosing unit'sdosage by means of the pressure on the basis of a prevailing temperatureof a surface or component of said exhaust duct.

The SCR system may comprise means for determining a prevailingtemperature of a surface or component of said exhaust duct.

The SCR system may comprise means for controlling the pressure byaltering a constriction in a reducing agent feedback line from thedosing unit to said container.

The SCR system may comprise means for controlling the pressure byaltering the configuration of the dosing unit.

The SCR system may comprise means for controlling the dosing unit'sdosage by means of the pressure on the basis of a prevailing temperatureof a surface in the exhaust system.

The SCR system may further comprise means for detecting a prevailingtemperature of a surface in the exhaust system. It may comprise meansfor determining a prevailing temperature of a surface in the exhaustsystem. It may comprise means for determining a prevailing temperatureof a surface in an exhaust duct which is provided to lead exhaust gasesfrom an engine to the surroundings.

The SCR system may comprise means for determining a prevailingtemperature of a silencer of an exhaust system. It may comprise meansfor determining a prevailing temperature of a suitable component of asilencer of an exhaust system.

The SCR system may comprise means for calculating a prevailingtemperature of a suitable surface in the exhaust system. It may comprisemeans for calculating a prevailing temperature of a surface in theexhaust system where reducing agent dosed at least partly vaporises.Said calculation may be based on specified parameters, e.g. exhaust massflow and exhaust temperature.

The SCR system may comprise means for controlling the dosing unit'sdosage by means of the pressure on the basis of a prevailing temperatureof an exhaust flow from an engine and/or a prevailing mass flow ofexhaust gases from an engine.

The SCR system may further comprise means for controlling the dosingunit's dosage by means of the pressure and a dosing cycle rate.

The SCR system may further comprise means for varying the pressure ofthe reductant within a range of 5-15 bar.

The SCR system may comprise means for varying the pressure of thereductant steplessly during said control of the dosing unit's dosage.

The SCR system may comprise means for varying the pressure of thereductant in discrete steps during said control of the dosing unit'sdosage.

The SCR system may comprise means for altering a dosing cycle ratesteplessly or in discrete steps during said control of the dosing unit'sdosage.

The SCR system may comprise means for controlling the dosing unit'sdosage by means of the pressure of the reductant and a dosing cycle rateon the basis of a prevailing exhaust temperature and/or a prevailingmass flow of exhaust gases from an engine of the vehicle.

The above objects are also achieved with a motor vehicle which isprovided with the SCR system. The vehicle may be a truck, bus or car.

One aspect of the invention is a proposed computer program for an SCRsystem, which program comprises program code stored on acomputer-readable medium for causing an electronic control unit oranother computer connected to the electronic control unit to performsteps according to the invention.

One aspect of the invention is a proposed computer program for an SCRsystem, which program comprises program code for causing an electroniccontrol unit or another computer connected to the electronic controlunit to perform steps according to the invention.

One aspect of the invention is a proposed computer program for an SCRsystem, which program comprises program code stored on a medium forcausing an electronic control unit or another computer connected to theelectronic control unit to perform steps according to the invention.

One aspect of the invention is a proposed computer program productcomprising a program code stored on a computer-readable medium forperforming method steps according to the invention when said computerprogram is run on an electronic control unit or another computerconnected to the electronic control unit.

Further objects, advantages and novel features of the present inventionwill become apparent to one skilled in the art from the followingdetails, and also by putting the invention into practice. Whereas theinvention is described below, it should be noted that it is not confinedto the specific details described. One skilled in the art having accessto the teachings herein will recognise further applications,modifications and incorporations within other fields, which are withinthe scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

For fuller understanding of the present invention and its furtherobjects and advantages, the detailed description set out below should beread in conjunction with the accompanying drawings, in which the samereference notations pertain to similar items in the various diagrams and

FIG. 1 schematically illustrates a vehicle according to an embodiment ofthe invention,

FIG. 2 schematically illustrates a subsystem for the vehicle depicted inFIG. 1, according to an embodiment of the invention,

FIG. 3 a is a schematic flowchart of a method according to an embodimentof the invention,

FIG. 3 b is a more detailed schematic flowchart of a method according toan embodiment of the invention, and

FIG. 4 schematically illustrates a computer according to an embodimentof the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a side view of a vehicle 100. The vehicle hereexemplified comprises a tractor unit 110 and a trailer 112. The vehiclemay be a heavy vehicle, e.g. a truck or a bus. It may alternatively be acar.

It should be noted that the invention is suitable for application in anySCR system and is therefore not confined to SCR systems for motorvehicles. The innovative method and the innovative SCR system accordingto one aspect of the invention are well suited to other platforms whichcomprise an SCR system than motor vehicles, e.g. watercraft. Thewatercraft may be of any kind, e.g. motorboats, steamers, ferries orships.

The innovative method and the innovative SCR system according to oneaspect of the invention are for example also well suited to systemswhich comprise industrial engines and/or engine-powered industrialrobots.

The innovative method and the innovative SCR system according to oneaspect of the invention are also well suited to various kinds of powerplants, e.g. an electric power plant provided with a diesel generator.

The innovative method and the innovative SCR system are well suited toany engine system which comprises an engine and an SCR system, e.g. on alocomotive or some other platform.

The innovative method and the innovative SCR system are well suited toany system which comprises an NO_(x) generator and an SCR system.

The term “link” refers herein to a communication link which may be aphysical connection such as an opto-electronic communication line, or anon-physical connection such as a wireless connection, e.g. a radio linkor microwave link.

The term “line” refers herein to a passage for holding and conveying afluid, e.g. a reducing agent in liquid form. The line may be a pipe ofany size and be made of any suitable material, e.g. plastic, rubber ormetal.

The term “reductant” or “reducing agent” refers herein to an agent usedfor reacting with certain emissions in an SCR system. These emissionsmay for example be NOx gas. The terms “reductant” and “reducing agent”are herein used synonymously. In one version, said reductant isso-called AdBlue. Other kinds of reductants may of course be used.AdBlue is herein cited as an example of a reductant, but one skilled inthe art will appreciate that the innovative method and the innovativedevice are feasible with other types of reductants, subject to necessaryadaptations, in control algorithms in accordance with the innovativemethod.

The term “cycle rate” refers herein to a rate defined by the number ofdosing periods, also called dosing cycles, per second. It should howeverbe noted that at least one active dose of reducing agent from the dosingunit may take place during a dosing cycle.

The term “pressure of the reductant” refers herein to a pressure atwhich said reductant is dosed from a dosing unit of the innovative SCRsystem. The pressure at which said reductant is dosed, and the workingpressure Pr, are herein used synonymously.

FIG. 2 depicts a subsystem 299 of the vehicle 100. The subsystem 299 issituated in the tractor unit 110 and may be part of an SCR system. Itcomprises in this example a container 205 arranged to hold a reductant.The container is adapted to holding a suitable amount of reductant andalso to being replenishable as necessary.

A first line 271 is provided to lead the reductant to a pump 230 fromthe container 205. The pump 230 may be any suitable pump. It may be adiaphragm pump with at least one filter. It may be arranged to be drivenby an electric motor (not depicted). The pump is adapted to drawing thereductant from the container 205 via the first line 271 and supplying itvia a second line 272 to a dosing unit 250. The dosing unit comprises anelectrically controlled dosing device by means of which a flow ofreductant added to the exhaust system can be controlled. The dosing unitcomprises an electrically controlled dosing valve by means of which aflow of reductant added to the exhaust system can be controlled. Thepump is adapted to pressurising the reductant in the second line 272.The dosing unit is provided with a throttle unit, which may also becalled throttle valve, against which said pressure of the reductant maybuild up in the subsystem 299. This pressure is herein referred to asthe working pressure Pr of the SCR system. Said throttle unit may be ofa fixed or adjustable type.

The dosing unit 250 is adapted to supplying said reductant to an exhaustsystem of the vehicle 100. More specifically, it is adapted to supplyinga suitable amount of reductant in a controlled way to an exhaust duct290 of the vehicle 100. In this version, an SCR catalyst (not depicted)is situated downstream of a location in the exhaust system where thesupply of reductant takes place. The amount of reductant supplied in theexhaust system is intended to be used in the SCR catalyst for reducingthe amount of unacceptable emissions.

The dosing unit 250 may be situated adjacent to said exhaust duct 290which is provided to lead exhaust gases from a combustion engine (notdepicted) of the vehicle to the SCR catalyst and thence to the vehicle'ssurroundings. A third line 273 running between the dosing unit 250 andthe container 205 is adapted to leading back to the container a certainamount of the reductant fed to the dosing valve 250. This configurationresults in advantageous cooling of the dosing unit 250. The dosing unitis thus cooled by a flow of the reductant when it is pumped through itfrom the pump 230 to the container 205.

A first control unit 200 is arranged for communication with a pressuresensor 220 via a link 221. This pressure sensor is adapted to detectinga prevailing pressure Pr of the reductant at the location where thesensor is fitted. In this version the sensor is situated adjacent to thesecond line 272 to measure the working pressure Pr of the reductantdownstream of the pump 230. In another version it is situated in thedosing unit 250 to measure the working pressure Pr of the reductantdownstream of the pump. It is adapted to continuously sending signalsvia the link 221 to the first control unit 200 which contain informationabout a prevailing pressure Pr of the reductant.

The first control unit 200 is arranged for communication with the pump230 via a link 231 and is adapted to controlling the operation of thepump. In one example the first control unit is adapted to controllingthe pump by means of an electric motor. The first control unit isadapted to influencing the working pressure Pr in the second line 272,which may be achieved in various suitable ways.

In one example, the first control unit 200 is adapted to altering aprevailing rotation speed RPM of the pump 230, making it possible forthe pressure Pr to be altered in desirable ways. It may be raised byincreasing the speed of the pump. It may be lowered by reducing thespeed of the pump.

In another example, the first control unit 200 may be adapted toinfluencing the pressure Pr by controlling a change in the stroke lengthof a piston or a diaphragm of the pump 230. By altering an internalconfiguration or internal geometry of the pump it is also possible forthe pressure Pr to be varied while maintaining a substantially constantspeed RPM of the pump. The pressure may thus for example be influencedby altering a stroke length of pistons or diaphragms of the pump.

The first control unit 200 is arranged for communication with a firsttemperature sensor 240 via a link 241. This sensor is adapted todetecting a prevailing temperature T1 of an exhaust flow from thevehicle's engine. In one example this first sensor is situatedimmediately downstream of the vehicle's engine and upstream of a dosingunit 250. It is adapted to continuously detecting a prevailingtemperature T1 of the exhaust flow and sending signals which containinformation about said prevailing temperature to the first control unitvia the link 241.

The first control unit 200 is arranged for communication with a secondtemperature sensor 260 via a link 261. This sensor is adapted todetecting a prevailing temperature T2 of a surface in the exhaust systemwhere the reducing agent vaporises. In one example this second sensor issituated directly downstream of a dosing unit 250. In another example itis situated in a vaporisation unit 270 downstream of the dosing unit.This second sensor is adapted to continuously detecting a prevailingtemperature T2 of a surface and sending signals which containinformation about said temperature to the first control unit via thelink 261.

The first control unit 200 is arranged for communication with the dosingunit 250 via a link 251 and is adapted to controlling the operation ofthe dosing unit, e.g. in order to regulate the supply of reductant tothe vehicle's exhaust system.

The dosing unit 250 may be provided with a nozzle to dose the reductantfor mixing with exhaust gases in an exhaust system of the vehicle. Inone version a geometry of said nozzle may be variable, making itpossible to control the pressure Pr of the reductant. The first controlunit 200 is adapted to altering said variable configuration of thedosing unit in order to control the pressure Pr of the reductant.

The first control unit 200 is adapted in one version to using thesignals received from the pressure sensor 220 which contain informationabout a prevailing pressure of the reductant as a basis for running saidpump 230 in a manner in accordance of one aspect of the innovativemethod. Feedback control of the working pressure Pr is thus achieved.

The first control unit 200 is adapted to calculating an exhaust massflow MF of the exhaust gases from the vehicle's engine. It is adapted tocontinuously determining an exhaust mass flow MF of the exhaust gasesfrom the vehicle's engine. This may be achieved in any suitable way.

In one version the subsystem comprises a mass flow sensor (not depicted)adapted to continuously measuring a prevailing exhaust mass flow fromthe vehicle's engine. Said sensor is adapted to continuously sendingsignals which contain information about a prevailing exhaust mass flowto the first control unit via a link.

The first control unit 200 is adapted to controlling the dosage of thedosing unit 250 by means of a pressure Pr at which reducing agent isdosed. It may be adapted to controlling the pressure Pr by control ofthe speed RPM of the pump 230. It may be adapted to controlling thepressure Pr by altering a constriction in the line 273 for reducingagent from the dosing unit 250 to the container 205. In one alternative,the first control unit is adapted to controlling the pressure Pr byaltering a constriction of reducing agent flow in the dosing unit 250,which flow is intended to lead to the container 205. It may be adaptedto controlling the pressure Pr by altering the configuration of thedosing device of the dosing unit. It may adapted to controlling thedosing unit's dosage by means of the pressure Pr on the basis of aprevailing temperature T1 of an exhaust flow from an engine and/or aprevailing mass flow MF of exhaust gases from an engine. It may beadapted to controlling the dosing unit's dosage by means of the pressurePr of the reductant and a dosing cycle rate CF. It may be adapted tovarying the pressure Pr of the reductant within a range of 5-15 bar. Itmay be adapted to varying the pressure Pr of the reductant steplesslyduring said control of the dosing unit's dosage. It may be adapted tovarying the pressure Pr of the reductant in discrete steps during saidcontrol of the dosing unit's dosage. It may be adapted to altering adosing cycle rate CF steplessly or in discrete steps during said controlof the dosing unit's dosage. It may adapted to controlling the dosingunit's dosage by means of the pressure Pr of the reductant and a dosingcycle rate CF on the basis of a prevailing exhaust temperature T1 and/ora prevailing exhaust mass flow MF of exhaust gases from an engine of thevehicle. It is adapted to controlling the dosing unit's dosage by meansof a pressure Pr at which reducing agent is dosed, which pressure iscontrolled by control of a speed (RPM) of said feed device 230. Thefirst control unit is adapted to controlling the dosing unit's dosage bymeans of the pressure on the basis of a prevailing temperature T2 of asurface or component of said exhaust duct 290.

A second control unit 210 is arranged for communication with the firstcontrol unit 200 via a link 201. This second control unit may bedetachably connected to the first control unit. It may be a control unitexternal to the vehicle. It may be adapted to conducting the innovativemethod steps according to the invention. It may be used to cross-loadsoftware to the first control unit, particularly software for applyingthe innovative method. It may alternatively be arranged forcommunication with the first control unit via an internal network of thevehicle. It may be adapted to performing functions substantially similarto the first control unit, e.g. controlling the dosing unit's dosage bymeans of a pressure Pr at which reducing agent is dosed. The innovativemethod may be conducted by the first control unit 200 or the secondcontrol unit 210 or by both of them.

Some examples appear below of how the working pressure Pr may becontrolled by the first control unit 200 in various different operatingsituations of the vehicle 100.

Example 1

A change from a reference state to a state with higher exhausttemperature T and greater exhaust mass flow MF (e.g. T>400 degrees C.and MF>1000 kg/h) is here determined. The working pressure Pr is thuslowered (e.g. from 9 to 5 bar) to achieve dosage in larger drops ofreducing agent which may be directed better in the large exhaust flowand encounter desired warm surface in the vehicle's exhaust system.Controlled wall encounter is thus advantageously achieved.

Example 2

A change from a reference state to a state with higher exhausttemperature T and smaller exhaust mass flow (e.g. T>400 degrees C. andMF<1000 kg/h) is here determined. The working pressure Pr is thus raised(e.g. from 9 to 15 bar) to achieve dosage in smaller drops of reducingagent which may vaporise immediately in the exhaust flow before theyencounter a surface in the vehicle's exhaust system. Improvedvaporisation of reducing agent before wall encounter is thusadvantageously achieved.

Example 3

A change from a reference state to a state with lower exhausttemperature T and greater exhaust mass flow MF (e.g. T<250 degrees C.and MF>1000 kg/h) is here determined. The working pressure Pr may herebe kept at a reference level (e.g. 9 bar) to achieve a drop sizedistribution which comprises both large and small drops of reducingagent. This means that certain drops may be entrained by the exhaustflow while others may be directed by the flow. A large encounter surfacein the vehicle's exhaust system is thus achieved for best possibleutilisation of thermal energy available therein and prevention of localcooling.

Example 4

A change from a reference state to a state with lower exhausttemperature T and smaller exhaust mass flow MF (e.g. T<250 degrees C.and MF<1000 kg/h) is here determined. The working pressure Pr may herebe raised to achieve small drops which may vaporise more quickly on thesurfaces encountered in the exhaust system or may actually vaporise inthe exhaust flow. The result is rapid vaporisation in the exhaust and/oron surfaces in the exhaust system when this operating situation hasleast thermal energy available for vaporisation of said reducing agent.

In a case of transient operation, the method may be supplemented so thatcontrol is based on a preceding operating situation. In one exampleafter a lengthy period of operation with relatively high exhausttemperature T and a relative large exhaust flow the vehicle's exhaustsystem may still be warm despite a prevailing exhaust mass flow and aprevailing exhaust temperature both being low at the time. Acorresponding earlier prevailing working pressure may thus withadvantage continue to be utilised for an appropriate period of time.

In one aspect of the invention the working pressure Pr may be controlledon the basis of a change in a detected exhaust backpressure of thevehicle. In response to an increase in such a backpressure the workingpressure may with advantage be raised in a suitable way to maintain adesired spray pattern of reducing agent dosed.

In one aspect of the invention the working pressure Pr may be controlledon the basis of a prevailing temperature of air surrounding the vehicle.

In a situation where the temperature of the surrounding air is below 0degrees C. the working pressure may be raised as appropriate, e.g. by 2bar, to alter the drop size distribution towards smaller drops and thuspotentially facilitate vaporisation of reducing agent dosed.

In one aspect of the invention the working pressure Pr may be controlledon the basis of a prevailing temperature of the reducing agent in thevehicle's SCR system.

In a situation where the prevailing temperature of the reducing agent isfor example above 50 degrees C., the working pressure may be lowered asappropriate, e.g. by 2 bar, to compensate for a faster vaporisation ratecaused by the warm reducing agent.

FIG. 3 a is a schematic flowchart of a method pertaining to SCR systemsfor a motor vehicle, comprising a feed device to feed reducing agentfrom a container to a dosing unit for supply of said reducing agent toan exhaust duct of the vehicle, according to an embodiment of theinvention. The method comprises a first step s301 comprising the step ofcontrolling the dosing unit's dosage by means of a pressure at whichreducing agent is dosed. The method ends after step s301.

FIG. 3 b is a schematic flowchart of a method pertaining to SCR systemsfor a motor vehicle, comprising a feed device to feed reducing agentfrom a container to a dosing unit for supply of said reducing agent toan exhaust duct of the vehicle, according to an embodiment of theinvention.

The method comprises a first step s310 comprising the step ofdetermining a prevailing temperature T1 of exhaust gases from the engineof the vehicle 100. This may be effected by means of the temperaturesensor 240. Step s310 is followed by a step s320.

Method step s320 comprises the step of determining a prevailing massflow MF of said exhaust gases. This exhaust mass flow may in one examplebe calculated by the first control unit 200. Alternatively it may bedetected by means of suitable sensors or equipment. Step s320 isfollowed by a step s330.

Method step s330 comprises the step of controlling the dosage of thedosing unit 250 by means of a pressure Pr at which reducing agent isdosed. This pressure may be altered by influencing a speed of the pump230. It may alternatively or in combination be altered by acting upon aconstriction in the line 273. It may alternatively or in combination bealtered by altering the configuration of the dosing unit's dosingdevice.

In one version, the dosage of the dosing unit 250 is controlled by meansof the pressure Pr on the basis of a said prevailing temperature T1determined of the exhaust flow and/or on the basis of said prevailingexhaust mass flow MF determined.

Step s330 is followed by a step s340.

Method step s340 comprises the step of controlling the dosage of thedosing unit 250 by means of a cycle rate of the SCR system. In oneversion said control of the dosing unit's dosage is by means of thepressure Pr at which reducing agent is dosed, at the same time as saidcontrol of the dosing unit's dosage by means of a cycle rate of the SCRsystem.

In one version, the dosage of the dosing unit 250 is controlled by meansof the pressure Pr of the reductant and by means of a dosing cycle rateCF at the same time on the basis of said prevailing exhaust temperatureT1 determined and/or said prevailing exhaust mass flow MF determined.

The method ends after step s340.

FIG. 4 is a diagram of one version of a device 400. The control units200 and 210 described with reference to FIG. 2 may in one versioncomprise the device 400. The device 400 comprises a non-volatile memory420, a data processing unit 410 and a read/write memory 450. Thenon-volatile memory has a first memory element 430 in which a computerprogram, e.g. an operating system, is stored for controlling thefunction of the device 400. The device 400 further comprises a buscontroller, a serial communication port, I/O means, an A/D converter, atime and date input and transfer unit, an event counter and aninterruption controller (not depicted). The non-volatile memory has alsoa second memory element 440.

A proposed computer program P comprises routines for controlling thedosage of the dosing unit 250 by means of a pressure Pr at whichreducing agent is dosed. The program comprises routines for controllingthe pressure Pr by control of the speed RPM of the pump 230. The programcomprises routines for controlling the pressure Pr by altering aconstriction in the line 273 for reducing agent from the dosing unit 250to the container 205. In one alternative, the program comprises routinesfor controlling the pressure Pr by altering a constriction of reducingagent flow in the dosing unit, which flow is intended to lead to thecontainer. The program comprises routines for controlling the pressurePr by altering the configuration of the dosing device of the dosingunit. The program comprises routines for controlling the dosing unit'sdosage by means of the pressure Pr on the basis of a prevailingtemperature T of an exhaust flow from an engine and/or a prevailing massflow MF of exhaust gases from an engine. The program comprises routinesfor controlling the dosing unit's dosage by means of the pressure Pr ofthe reductant and a dosing cycle rate CF. The program comprises routinesfor varying the pressure Pr of the reductant within a range of [5, 15]bar. The program comprises routines for varying the pressure Pr of thereductant steplessly during said control of the dosing unit's dosage.The program comprises routines for varying the pressure Pr of thereductant in discrete steps during said control of the dosing unit'sdosage. The program comprises routines for altering a dosing cycle rateCF steplessly or in discrete steps during said control of the dosingunit's dosage. The program comprises routines for controlling the dosingunit's dosage by means of the pressure Pr of the reductant and a dosingcycle rate CF on the basis of a prevailing exhaust temperature T and/ora prevailing exhaust mass flow MF of exhaust gases from an engine of thevehicle. The program comprises routines for controlling the dosingunit's dosage by means of a pressure Pr at which reducing agent isdosed, which pressure is controlled by control of a speed (RPM) of saidfeed device 230. The program comprises routines for controlling thedosing unit's dosage by means of the pressure on the basis of aprevailing temperature T2 of a surface or component of said exhaust duct290.

The program P may be stored in an executable form or in compressed formin a memory 460 and/or in a read/write memory 450.

Where the data processing unit 410 is described as performing a certainfunction, it means that the data processing unit conducts a certain partof the program stored in the memory 460, or a certain part of theprogram stored in the read/write memory 450.

The data processing device 410 can communicate with a data port 499 viaa data bus 415. The non-volatile memory 420 is intended forcommunication with the data processing unit 410 via a data bus 412. Theseparate memory 460 is intended to communicate with the data processingunit 410 via a data bus 411. The read/write memory 450 is adapted tocommunicating with the data processing unit via a data bus 414. The dataport 499 may for example have the links 201, 221, 231, 241 and 251connected to it (see FIG. 2).

When data are received on the data port 499, they are temporarily storedin the second memory element 440. When input data have been storedtemporarily, the data processing unit 410 is prepared to effect codeexecution as described above. In one version, signals received on thedata port 499 contain information about a prevailing working pressure Prof the reductant in the SCR system. In one version, signals received onthe data port contain information about a prevailing temperature T1 ofthe exhaust gases in an exhaust system of the vehicle. In one version,signals received on the data port contain information about a prevailingmass flow MF of the exhaust gases in an exhaust system of the vehicle.

The signals received on the data port 499 may be used by the device 400to apply the herein innovative method.

Parts of the methods herein described may be conducted by the device 400by means of the data processing unit 410 which runs the program storedin the memory 460 or the read/write memory 450. When the device 400 runsthe program, methods herein described are executed.

The foregoing description of the preferred embodiments of the presentinvention is provided for illustrative and descriptive purposes. It isnot intended to be exhaustive nor to restrict the invention to thevariants described. Many modifications and variations will obviouslysuggest themselves to one skilled in the art. The embodiments have beenchosen and described in order best to explain the principles of theinvention and their practical applications and hence make it possiblefor one skilled in the art to understand the invention for differentembodiments and with the various modifications appropriate to theintended use.

1. A method pertaining to an SCR system for a motor vehicle comprisingan engine having an exhaust duct; a feed device configured to feed areducing agent from a container to a dosing unit for supply of thereducing agent to the exhaust duct of the vehicle, the feed device beingrotatable in a path of the reducing agent to the dosing unit, therotation being at a controllable rotation speed; the method comprising,controlling a dosage of the reducing agent supplied by the dosing unitby controlling a pressure (Pr) at which the reducing agent is dosed, andcontrolling the pressure (Pr) by control of the rotation speed of thefeed device.
 2. A method according to claim 1, in which the systemfurther comprises a feedback line for reducing agent from the dosingunit to the container and an alterable constriction in the feedbackline; the method further comprising controlling the pressure (Pr) byaltering the constriction in the feedback line.
 3. A method according toclaim 1, further comprising controlling the pressure (Pr) by alteringthe configuration of the dosing unit.
 4. A method according to claim 1,further comprising controlling the dosage of the dosing unit by means ofthe pressure (Pr) based on a prevailing temperature (T2) of a surface ora component of the exhaust duct (290).
 5. A method according to claim 1,further comprising controlling the dosage of the dosing unit by means ofthe pressure (Pr) based on a prevailing temperature (T1) of an exhaustflow from the engine and/or a prevailing mass flow (MF) of exhaust gasesfrom the engine.
 6. A method according to claim 1, further comprisingcontrolling the dosage of the dosing unit by means of the pressure (Pr)and a dosing cycle rate (CF).
 7. A method according to claim 1, furthercomprising the varying the pressure (Pr) of the reducing agent is withina range of 5-15 bar.
 8. A method according to claim 1, furthercomprising controlling the dosage of the dosing unit by means of thepressure (Pr) and a dosing cycle rate (CF) on the basis of a prevailingexhaust temperature (T) and/or a prevailing mass flow (MF) of exhaustgases from the engine of the vehicle.
 9. An SCR system for a motorvehicle comprising: a feed device configured to feed reducing agent froma container to a dosing unit for supply of the reducing agent to anexhaust duct of the vehicle; the feed device being rotatable in a pathof the reducing agent to the dosing unit, the rotation being at acontrollable rotation speed; a control device for controlling a dosageof the dosing unit by means of a pressure (Pr) at which the reducingagent is dosed, and and the control device being configured forcontrolling the pressure by control of a rotation speed (RPM) of thefeed device.
 10. An SCR system according to claim 9, further comprising:a feedback line for reducing agent from the dosing unit to the containerand an alterable constriction in the feedback line; the control devicebeing configured for controlling the pressure (Pr) by altering theconstriction in a feedback line for the reducing agent from the dosingunit to the container.
 11. An SCR system according to claim 9, furthercomprising the control device being configured for controlling thepressure (Pr) by altering the configuration of the dosing unit.
 12. AnSCR system according to claim 9, further comprising the control devicebeing configured for controlling the dosage of the dosing unit by meansof the pressure (Pr) based on a prevailing temperature (T2) of a surfaceor a component of the exhaust duct.
 13. An SCR system according to claim12, further comprising a sensor for determining a prevailing temperature(T2) of a surface or component of the exhaust duct.
 14. An SCR systemaccording to claim 9, further comprising the control device beingconfigured for controlling the dosage of the dosing unit by means of thepressure (Pr) based on a prevailing temperature (T1) of an exhaust flowfrom the engine and/or a prevailing mass flow (MF) of exhaust gases fromthe engine.
 15. An SCR system according to claim 9, further comprisingthe control device being configured for controlling the dosage of thedosing unit by means of the pressure (Pr) and a dosing cycle rate (CF).16. An SCR system according to claim 9, further comprising the controldevice being configured for varying the pressure (Pr) of the reductantwithin a range of 5-15 bar.
 17. An SCR system according to claim 9,further comprising the control device being configured for controllingthe dosage of the dosing unit by means of the pressure (Pr) and a dosingcycle rate (CF) on the basis of a prevailing exhaust temperature (T)and/or a prevailing mass flow (MF) of exhaust gases from the engine ofthe vehicle.
 18. A motor vehicle provided with an SCR system accordingto claim
 9. 19. A motor vehicle according to claim 18, comprising anyfrom among a truck, bus or car.
 20. (canceled)
 21. A computer programproduct pertaining to an SCR system, the system comprising a feed deviceto feed reducing agent from a container to a dosing unit for supply ofthe reducing agent to an exhaust duct of a vehicle; the program productcomprising a program code stored on a non-volatile computer-readablemedium wherein the program comprises program code for causing anelectronic control unit or another computer connected to the electroniccontrol unit to perform steps according to claim 1 for when the computerprogram is run on the electronic control unit or another computerconnected to the electronic control unit.